Fertile Ground for a Microgrid

by Cathy Cash

February 26, 2018February 28, 2018

Gas from waste lagoons on Butler Farms in Harnett County, North Carolina, helps power a microgrid that includes biogas, solar, diesel generation, and battery storage. The farm’s population of 7,500 to 8,000 swine yields some 9,000 gallons of hog waste per day. (Photo courtesy North Carolina EMC)

Tom Butler didn’t intend to build a microgrid.

He’d originally thought covering the waste lagoons at his nearly 100-year-old family hog farm in Lillington, North Carolina, would help mitigate some of the negative effects the facility may have had on the community.

“We were a little naive about environmental impacts” in the early days, Butler says. “We want to lessen the impact in the future.”

Like most hog farms in North Carolina—the nation’s fourth-largest hog producer—the Butler operation stores waste from livestock in a lagoon. A population of 7,500 to 8,000 swine creates about 9,000 gallons of waste a day.

Covering the lagoons in 2008 greatly reduced odors from the farm, and Butler could use the captured methane to generate electricity. He consulted with his electric co-op, South River EMC in Dunn, in developing the local generation project.

“We’re taking a waste product and making it an asset,” he says. “It makes the waste a positive rather than a negative.”

Butler’s biogas system added 185 kW of generation to the farm on top of 100 kW of capacity from an existing diesel generator. Soon after the biogas project was complete, he installed 20 kW of solar power.

Nearly 10 years later, Butler began working with South River EMC and Raleigh-based North Carolina Electric Membership Corporation (NCEMC; statewide/G&T) to expand the project into something bigger: a functioning microgrid.

NCEMC installed a 250-kW/735-kWh battery system and a microgrid-control system that integrates and manages all components.

During normal conditions or at peak times, the Butler microgrid will feed into the South River EMC system; during an outage, it can power the farm and about 28 neighboring homes for four hours or longer, depending on what generation resources are available onsite. As the system matures, South River EMC will look to expand the impact beyond these homes.

“The Butler Farms microgrid serves as a case study for how agriculture and electric utilities—two of North Carolina’s most important industries—can work together to promote sustainability and improve quality of life in rural North Carolina and for electric cooperative members,” says John Lemire, director of Transmission Resources for NCEMC.

On-site prep work and testing took place in 2017, and the first phase of the microgrid is set to begin operation early this year.